From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D5DE0CD37B5 for ; Mon, 11 May 2026 10:27:41 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wMNrG-000149-S5; Mon, 11 May 2026 06:27:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wMNr5-0000zv-AS for qemu-devel@nongnu.org; Mon, 11 May 2026 06:27:21 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wMNr3-0000ZJ-AK for qemu-devel@nongnu.org; Mon, 11 May 2026 06:27:19 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1778495235; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=ZJ+puVqsXjYx3RtmQGGoQag+v2327RJpj+NwSKlM47k=; b=TecVhkovKbXKmC1MKoiohkAatQM1ipUrHQAaC8xylcFN/Gj8lyizkjWS9IHnD6fY1cOPSF /1yvM2dtmVQ89vqRtm01LcIoSzRHj06nBXhAZlMGqFR0tuOnXdYFA37Cq2bY50VQtBlwQL REc8ZpGLYCst0F26qBcibgiE8hX5FTg= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-185-6QuLEpwzMfuaWGPfKLWZPA-1; Mon, 11 May 2026 06:27:14 -0400 X-MC-Unique: 6QuLEpwzMfuaWGPfKLWZPA-1 X-Mimecast-MFC-AGG-ID: 6QuLEpwzMfuaWGPfKLWZPA_1778495233 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E969718005B4; Mon, 11 May 2026 10:27:12 +0000 (UTC) Received: from redhat.com (unknown [10.44.50.30]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5CF0019560A6; Mon, 11 May 2026 10:27:10 +0000 (UTC) Date: Mon, 11 May 2026 11:27:06 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Paolo Bonzini Cc: Jinjie Ruan , peter.maydell@linaro.org, mst@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH v2] hw/rtc/mc146818rtc: Fix get_guest_rtc_ns() overflow bug Message-ID: References: <20260114013257.3500578-1-ruanjinjie@huawei.com> <92cecc93-1f68-44f2-8d0b-934e868d3e2c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <92cecc93-1f68-44f2-8d0b-934e868d3e2c@redhat.com> User-Agent: Mutt/2.3.1 (2026-03-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, May 11, 2026 at 09:06:54AM +0200, Paolo Bonzini wrote: > On 1/14/26 02:32, Jinjie Ruan wrote: > > In get_guest_rtc_ns(), "s->base_rtc" is uint64_t, which multiplied by > > "NANOSECONDS_PER_SECOND" may overflow the uint64_t type, which will > > cause the QEMU Linux Virtual Machine's RTC time to jump and in turn > > triggers a kernel Soft Lockup and ultimately leads to a crash. > > > > Fix it by avoiding adding s->base_rtc in get_guest_rtc_ns_offset(), > > because get_guest_rtc_ns() is used either take the remainder of > > NANOSECONDS_PER_SECOND or take the quotient of NANOSECONDS_PER_SECOND. > > > > Fixes: 56038ef6234e ("RTC: Update the RTC clock only when reading it") > > Signed-off-by: Jinjie Ruan > > Thanks, queued - I also renamed the function to > get_rtc_ns_since_last_update(). It's not entirely accurate due the presence > of the sub-second offset s->offset, but it's good enough. > > I have also considered changing the function to return a struct timespec. I > didn't like it too much because struct timespec uses a time_t which is > possibly 32-bit. Now, QEMU is probably broken for Y2038 anyway, but having > time_t dependencies in device emulation code is not great; at least mktimegm > and gmtime_r could be rewritten easily. For system mode at least, we can assume time_t will be 64-bit only since we drop 32-bit host OS support. For user mode, we can likewise assume 64-bit host OS, but still have to deal with potential 32-bit time_t for the guest OS. One could argue that in the user mode case though, the guest ABI is what is broken for Y2038 - QEMU is just honouring the (broken) ABI that is defined. The tools could be impacted by 32-bit issues I guess, but we still have 10+ years to kill off the 32-bit host OS build support for tools With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|